My primary objective is to increase our understanding of the mechanisms whereby certain hormones exert their effects on the cell. The hormones aldosterone and vasopressin are known to stimulate the resorption of sodium across the epithelial cells of the kidney tubules. Many investigators believe that aldosterone increases sodium resorption by increasing the number of passive ion transporters on the apical side of the epithelial cell, and that vasopressin indirectly stimulates these transporters by a cAMP-mediated process. I will attempt to purify this passive sodium transporter by means of a reconstitution assay, in order to permit the direct measurement of any hormone effects on either the amount or activity of the transporter. The reconstitution assay will employ the procedures currently in use to incorporate transport enzymes into proteoliposomes that accumulate the transported substances. In this case I will try to incorporate the passive sodium transporter extracted from either kidney plasma membrane or the membranes of other epithelial tissues into proteoliposomes that take up sodium in an amiloride sensitive process. (Amiloride is a specific inhibitor of sodium passive transport into epithelial cells). I also intend to study the effects of thyroid hormone on active ion transport. Certain investigators have determined that tri-iodothyronine stimulates the specific activity of Na, K ATPase in rat tissues, and that the thyroid hormone stimulation of respiration depends on this stimulation. I will try to determine whether this increase in Na, K ATPase activity represents a genuine increase in enzyme concentration or an alteration in the efficiency of the pump.